Use of Low Earth Orbit (LEO) satellite networks is a promising approach for global broadband communications in view of their low delay and bit error characteristics compared to Geostationary (GEO) satellites. Due to their orbit, the communication link between a ground terminal and an LEO satellite will be available periodically only for a few minutes. In order to provide continuous communication between ground terminals, the LEO satellites need to be interconnected via inter-satellite links (called crosslinks) and terminal-terminal data traffic will be muted over multiple satellites using these crosslinks. Typically, an LEO satellite network consists of multiple orbit planes, and each plane consists of multiple satellites. The satellite topology (neighbor relationship) within a plane remains invariant while inter-plane topology will change constantly; interplane crosslinks will be dynamically set up and removed. Terminal-satellite associations (uplink and downlink connectivity) will also be changing constantly.
Real-time management of such a dynamically changing network is a complex problem. Network configuration information for provisioning new user services including route information for user traffic needs to be uploaded to relevant payloads from the network operations center in the ground in a timely manner. The operations center needs to monitor the status and performance of payloads. When problems occur in the satellite network, the operations center needs to quickly determine the root cause of the problem and perform corrective actions. In addition to timeliness, management should be accomplished with network efficiency; i.e., satellite network bandwidth used for management communication should be as low as possible so that maximum network bandwidth is available for user traffic.
These two goals are difficult to achieve in a LEO satellite network if a centralized management architecture is employed. In the centralized architecture, all management functions are performed by a single management center in the ground that has direct connectivity only to a single payload at any given time. Hence, management traffic between the payloads and the center will need to traverse multiple crosslinks in the satellite network. This increases management communication delay as well as the crosslink bandwidth utilized for management traffic. These drawbacks can be overcome by employing a distributed management architecture. In this architecture, multiple management centers are deployed on the ground in various geographical locations to reduce management communication delay and crosslink bandwidth utilized for management traffic.
Employment of a distributed management architecture for LEO satellite networks is a challenging problem. Determination of how many management centers to deploy, where to deploy, and the payload distribution among these centers are important issues. In the case of GEO satellite networks, due to fixed terminal-satellite connectivity made possible by geosynchronous satellite orbit and the wide coverage area of each satellite, it is possible to deploy a few centers such that each center is in the coverage area of a satellite and each satellite has a center in its coverage area. This is not possible for LEO satellite networks due to the limited coverage area and the constantly changing coverage area of each satellite.
Several proposals have been made for distributed management for LEO satellite networks.
P. Todorova, in Network Management in LEO Satellite Networks, Proceedings of the 35th Hawaii International Conference on System Sciences, 2002 proposes a distributed management architecture for ATM LEO satellite networks. The distributed architecture is focused on the management functionality split between the LEO payloads and the Network Control Center (NCC) on the ground. Todorova does not address the concept of multiple management centers collectively managing the LEO satellite network. In this architecture, management traffic between payloads and the NCC will traverse multiple crosslinks. This architecture does not address our objectives of minimizing management communication latency and reducing crosslink bandwidth utilized by management traffic.
Wenbo et al., in Z. Wenbo, S. Peigen, Design of Communication Primitives for Satellite Network Management, 6th International Conference on Wireless Communications Networking and Mobile Computing (WiCOM), 2010, propose a distributed management architecture for satellite networks. In this architecture, there is a central manager and multiple intermediate managers on the ground. The central manager collects management information from satellites via the intermediate managers. The management domain of an intermediate manager is dynamically determined and the domain varies over time. Each intermediate manager broadcasts login packets. Satellite nodes that receive login packets register with an intermediate manager by responding to its login packet. If a satellite node receives login packets from multiple managers, it chooses the manager that can be reached with minimum delay. It does this by sending “delay test” packets and determining the delay. Based on its orbit, a satellite may register with different intermediate managers at different times. This approach ensures that management communication does not traverse crosslinks thus reducing management communication latency and overhead. But, this scheme requires that management centers are widely deployed across the globe such that each satellite will always have at least one management center within its coverage area. This tremendously increases the management system deployment cost and does not seem feasible from a commercial operations perspective.
Gounder et al. in V. V. Gounder, R. Prakash, H. Abu-Amara, Routing in LEO-Based Satellite Networks, 1999 describe a scheme where multiple management centers with ground stations are deployed in the ground for uploading routing tables to LEO satellites. A management center uploads updated routing tables to a satellite when the satellite passes over it. Thus, this scheme caters to situations where periodic uploading of configuration data to the satellites is adequate. In contrast, the present invention supports both such periodic updates as well as exchange of management data between the satellites and the management centers that have more stringent latency requirements, such as alarms and real-time configuration changes to the payloads for rapid provisioning of user services.
The distributed management scheme for LEO satellite networks that is described in the present invention differs from the previous solutions described in the prior art in the following ways:
Firstly, the previous solutions use either fixed associations between the management centers and satellites or constantly changing associations between them. The former approach increases management communication latency and overhead traffic on crosslinks. The latter approach reduces latency and overhead. But, since the domain of a management center changes periodically and the center has status and performance information concerning a payload only for a limited time, it is not possible for management centers to perform meaningful performance data aggregation and summarization.
Secondly, the scheme described in the present invention is a hybrid approach where the management center with which a payload communicates is dependent on the type of management communication. Routine management functions are performed based on fixed management associations while time critical management functions for a payload are performed by the nearest center. The benefits are reduced latency and overhead for management communications and management centers can perform performance data aggregation and summarization.
Thirdly, in the present invention, the nearest centers are predetermined by the central network operations center (NOC) leveraging the time deterministic topology changes that occur in an LEO satellite network. This avoids additional communication exchanges between payloads and management centers, such as those described in Wenbo et al.
The present invention is a management scheme that provides management agility with network efficiency while enabling management aggregation capabilities in the distributed centers to reduce the amount of management information exchanged between the distributed management centers and the central network operations center.